Relative risk of RA in women with a history of breast cancer (case–control study), adjusted for, age, country of birth, educational level, age at first birth, number of children and family history of breast cancer/ovarian cancer
| RA (n) | Controls (n) | OR (95% CI) | |
| Overall | 555 | 3193 | 0.87 (0.79 to 0.95) |
| Exposure variants | |||
| Breast cancer, 18–50 years | 123 | 761 | 0.82 (0.67 to 0.99) |
| Breast cancer, >50 years | 432 | 2432 | 0.89 (0.80 to 0.98) |
| Stage 0, 2002–2016 | 28 | 130 | 1.10 (0.73 to 1.65) |
| Stage 1, 2002–2016 | 110 | 530 | 1.04 (0.84 to 1.27) |
| Stage 2, 2002–2016 | 61 | 456 | 0.67 (0.51 to 0.87) |
| Stage 3, 2002–2016 | 9 | 33 | 1.35 (0.65 to 2.83) |
| Stage 4, 2002–2016 | 1 | 17 | 0.29 (0.04 to 2.19) |
| Outcome variants | |||
| RA, 18–49 years | 24 | 111 | 1.09 (0.70 to 1.71) |
| RA, 50–75 years | 357 | 2132 | 0.84 (0.75 to 0.94) |
| RA, >75 years | 174 | 950 | 0.91 (0.77 to 1.08) |
| Breast cancer 18–50 and RA >50 years | 99 | 650 | 0.77 (0.62 to 0.96) |
| Seronegative RA | 157 | 921 | 0.85 (0.71 to 1.01) |
| Seropositive RA | 367 | 2088 | 0.88 (0.78 to 0.98) |
RA, rheumatoid arthritis.